1. The purple line on the London Underground. This line stretches from Heathrow Airport in West London and goes across the city passing through major sites such as Piccadilly Circus (obvious), Arsenal's stadium, and terminates at Cockfosters.
2. A loose girl is more strung out than this line. (Piccadilly refers to upperclass gentlement who would pick one of the whores that hung out around the statue of Eros in Central London. The whores were nicknamed Dilly's).

Man, that bitch is like the Piccadilly Line, strung out from the airport to the north and working everywhere in between!